I will point out once again the documented experience of "trained professionals" who serve as NYC cops - volley fire from half a dozen who are NOT being controlled or directed WILL result in collateral hits on innocent bystanders.
If the perp is confronted by two "good guys" and they are positioned opposite each other then both are downrange of the other. What part of chaos don't we understand here? At that point a higher capacity gun isn't the answer, it's a problem and it's been seen as a problem in the hands of LEO's doing that. Not to forget they actually have some training for coordination in those scenarios - we as the common people never get any.
Do you go out with your clubbing buddies and practice shooter takedown scenarios on the range? If presented what appears to be a good shot would you take it even tho your best friend is downrange - aiming right back at you?
There is also the issue of not having the "god view" with 100% overhead perspective and absolute certainty what is happening. That other "good guy" might be the shooters partner and you'd be mistaken in not taking the shot. But, too bad, you are playing by the rules and they are not.
That one issue is the main problem - they get to shoot anyone anywhere, you can't. Do you need two or three families suing you in the aftermath plus the political fallout of being the poster child of poor tactics AND celebrated as an honorary member of the Bad Guys for killing innocent civilians?
Go read a Mas Ayoob book pls on the follow on consequences of being in an armed confrontation, even if you succeed and it all works out legally. It will take a chunk out of your life before the winds of rhetoric calm down, much less family and friends resolving how they have a killer in their midst at holiday get togethers.
Your personal stress reduction over the incident is going to likely cost some money in counseling, too. Oh yes it will - don't be in denial over that, too.
It boils down to the preferred response - and shooting up the place to confront the A team who is exercising their preplanned response by stopping the shooter immediately may well get you killed - by the cops entering the building. Why? Killers have high capacity magazines.
Like was said, you got a flashing red arrow over your head saying "Good Guy?" Nope, what you have is a GUN IN YOUR HAND and adrenaline laced cops bursting thru the door with the preconceived mental picture of shooting That Guy With A Gun In His Hand.
Again, the view that mag capacity is the answer is a total fail. Tactics are the answer and about the only response in shooting back you have is if you actually are toe to toe with the shooter - otherwise you don't and won't be a positive contribution to the situation.
You will just be another shooter and half the witnesses will point YOU out in a lineup.
This is the continued problem with gun enthusiasts - they are "gun enthusiasts" first and foremost, who focus on the gun and it's features. They are not enthusiasts of tactics and have no understanding of what to do or not in situations. When trainers come to PD's to introduce advanced shooting scenarios do you know what the #1 thing they teach cops? You can get shot no matter what, by anybody, anytime. The lesson plan is one Kobayashi Maru after another with no good answers, cops are getting plinked with paint ball or simunitions and it's one big ego let down by the end of the day. It seems you can't do anything right.
Until you have that training don't plan on doing anything right other than hunker down, get out, and fight only if you are cornered. Do we already have a thread on that? Yes.
Do we have dozens of threads on what gun, mag capacity, ammo, or type optic, goes to looking at the problem the exact wrong way.